This invention is concerned with wastewater treatment systems. In particular, the invention encompasses a conversion of a suction duct clarifier to a suction pipe clarifier in an efficient manner without the need for penetrating the floor of the clarifier tank.
Suction duct clarifiers do not elevate sludge collected by the rake arms, but instead include horizontal pipes that convey raked sludge into a center sludge collection drum that surrounds the center influent column, is sealed against the column and rotates along with the rake arms. A floor opening is located within the annular space emcompassed by the drum, and this provides a vertical duct for movement of the sludge from the drum down below the floor to a horizontal RAS return pipe that conveys the sludge out of the clarifier. This pipe is under suction, so that suction exists in the sludge collection drum and draws the sludge to that drum from suction ducts supported by the rake arms.
On the other hand, suction pipe clarifiers include a series of sludge uplifting pipes on each rake arm, which include horizontal and vertical sections that deliver sludge ultimately to an elevated sludge collection box positioned around the center influent column. Raked and collected sludge rises up through these pipes and into the sludge collection box, by differential hydraulic pressure, since the liquid level in the sludge collection box is lower than the liquid level in the tank. The collection box rotates along with the rake arms, and is sealed against the exterior surface of the center influent column. The influent column includes in its outer wall at least one opening, usually four, through which sludge from the collection box flows inwardly into the center of the influent column where it is delivered into a sludge discharge downpipe. The sludge delivered to the downpipe does not mingle with influent wastewater rising up through the influent column.
The sludge travels down the vertical sludge discharge pipe, which at its lower end extends down into the concrete basin floor to connect with an under-floor RAS return pipe that conveys the sludge out and away from the clarifier. Typically a pump is provided outside the clarifier to establish suction to help withdraw this sludge through the RAS pipe.
A significant number of treatment plants have undertaken to convert an existing suction duct clarifier to a suction pipe clarifier. To accomplish this requires removal of the equipment, including the central influent column, from the concrete basin floor. Then, the concrete must be partly demolished to provide for a conduit flow path from a new vertical sludge discharge pipe, for downward flow of sludge and for connecting this pipe under the concrete surface to the existing horizontal RAS return pipe a few feet away that will convey the sludge out of the clarifier. This conversion is disruptive and expensive. All this is in addition to the addition of a new elevated sludge collection box such as described above, positioned on the center column and located centrally inside the clarifier's feedwell. This is accompanied by a series of sludge uplift pipes connected to the rake arms to allow raked sludge to be delivered into the elevated sludge collection box.
Many treatment plants have been hesitant to make this desirable conversion because of the disruption, time required, and high cost.